The invention relates to a hydraulic system for the provision of pressures and volume flows in a double-clutch transmission, in particular for the provision of a first volume flow for cooling and lubricating a first clutch and for the provision of a second volume flow for cooling and lubricating a second clutch.
In addition to the cooling and lubrication of the clutches, in the double-clutch transmissions known from the prior art the hydraulic system also assumes further tasks. Thus, by means of the hydraulic system, the two clutches can be actuated automatically, and also the selection and deselection of gears of the double-clutch transmission takes place automatically via a plurality of shift actuators.
EP 1413803 describes a method for cooling the two clutches of a double-clutch transmission in a motor vehicle. For carrying out the method, in this case, a hydraulic system by means of which an oil volume flow is provided for each clutch is required. Thus, according to the method, the respective clutch is provided with a volume flow which is dependent on an oil sump temperature, on the temperature of the oil flowing from the respective clutch and on the power which is transmitted by the clutches. A regulating valve or the like must accordingly be provided for each volume flow so that the volume flows can be regulated as a function of the abovementioned factors.
DE 103 06 895 likewise describes a method for cooling the double clutch of a motor vehicle, here the two clutches being jointly acted upon by a single volume flow of a coolant. As compared with cooling by means of two volume flows, this simplifies the construction of the corresponding hydraulic system. However, it is not possible to cool and lubricate a clutch of the double-clutch transmission individually. Thus, in DE 103 06 895, it is proposed to interrupt the overall volume flow of cooling and lubrication, particularly at low temperatures, in order to reduce the drag torque caused by the coolant located in the clutch and therefore to simplify the selection of a gear. In this case, it would be sufficient to interrupt only the volume flow for the clutch which is assigned to that subtransmission of the double-clutch transmission in which a gear is to be selected.
The provision of volume flows for a clutch in each case thus allows a controlled cooling and lubrication of the two clutches with more degrees of freedom. As a rule, however, this leads to a higher number of hydraulic components and, in particular, to a higher number of costly regulating valves. Moreover, the design of the hydraulic system must take into account the fact that, in the event of a failure of one or more of its components, at least an emergency operation of the double-clutch transmission should be possible.